Stable lead alkyl compositions and a method for preparing the same



United States Patent STABLE LEAD ALKY'L COMPOSITIONS AND A METHOD FOR PREPARING THE SAlVlE Hymin Shapiro, Baton Rouge, La., and Herbert R. Neal,

Farming ton, Mich., assignors to Ethyl Corporation,

N ew. .York, N .Y., a corporation of Delaware N0 Drawing. Filed Dec. '8, 1959, Ser. No. 858,040 4 Claims. ('Cl. 260-437) v This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates to methods for inhibiting the. thermal decomposition of alkyllead corn'pounds when subjected to temperatures above 100 C., at which temperature thermal decomposition becomes appreciable.

Generally this invention contemplates inhibiting the thermal decomposition of alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical. g

More specifically, this invention in concerned with an improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. It is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending withother products in making commercial antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyllead compounds where the likelihood of thermal decomposition is more of a problem. I

As is well known, tetraalkyllead antiknock compounds generally are producedvby reacting a sodium-lead alloy with an alkyl halide, Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer a problem. However, the tetraalkyllead compound so produced is in admixture with various reaction by-products from which it must be separated. Separation is effected by vsteam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due tothe toxic and unstable nature of tetraalkyllead antiknock compounds, these distillationv and purification .operations are subject to many difliculties. v

In these distillation and purification operations meticulous temperature control and exact safety measures are of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperaturewhere thermal decomposition ubecomes appreciable, For example, decomposition of tetraethylleadoccurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetraethyllead from the reaction products accompanying its synthesis. At temperatures above 100 C. the decomposition rate increases logarithmically so that a point is soon reached where external heat is no longer required and decomposition becomes self-propagating.

Such likelihood of excessive decomposition is present also during blending, handling, storage, and transportation. Prior to diluting the alkyllead concentrate with scavengers, gasoline or other materials, the alkyllead compound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally well below that of decomposition. For example, in the purification step wherein the tetraethyllead concentrate is washed and blown with air at atmospheric temperature to remove impurities, a sudden increase in temperature may occur due to the oxidation of triethylbismuth which is present as an impurity. Also pumps used in handling tetraethyllead occasionally freeze and the friction developed may cause a local overheating to a temperature above the temperature of decomposition of the tetraethyllead. Faulty wiring, leaks onto steam pipes, and other accidental causes also may produce local overheating with resulting dangerous decomposition.

It is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated state-viz. separation, purification, blending, transportation, and storage-the likelihood of excessive thermaldecomposition must be provided for and effectively combatted. w 4

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: separation, purification, blending, transportation, and storage.

The above and other objects of this invention are accomplished by incorporating with alkyllead'compounds a relatively small quantity of a material which has the property of inhibiting alkyllead thermal decomposition. The foregoin'gobjects are also accomplished by conducting oneor more of the foregoing operations in the presence of such a material. The materials which have been found to possess the property are referred to hereinafter as tl'iermal stabilizers.

The thermal stabilizers of this invention are aryl carbinols which preferably contain from 7 to about 30 carbon atoms in the 'molecule. These thermal stabilizers whenused in amount varying from about 0.25 to about 10 percent by weight of the lead alkyl product are effective in substantially retarding or preventing thermal decomposition at temperatures above 100 C. for extended periods of time. 7 v

Another important feature of this invention is the fact that the foregoing thermal stabilizers are, in general, stable to heat, light, exposure to air, and other conditions to which alkyllead compounds may be subjected during their separation, purification, blending, transportation, and storage. 7 Thus, for example, the thermal stabiliz ers of this invention have no tendency to react to form gumsor other obnoxous reaction products in the alkyllead composition.

. Another important feature of this invention is that the foregoing thermal stabilizers are relatively inexpensive and easily made. A further advantage in their use is that they are not corrosive to metals used in fabricating alkyllead storage tanks, pipe lines, tank cars, storage drums, and the like.

Typical thermal stabilizers of this invention are phenyl carbinol; o-, m-,-and'p-tolyl carbinol; the xylyl carbinols; p-nonyl-phenyl carbinol; the naphthyl carbinols; 2,5-xylyl methyl carbinol; phenyl isopropyl carbinol; cumenyl tert-butyl carbinol; p-tolyl hexyl carbinol; diphenyl carbinol; the ditolyl carbinols, the dinaphthyl carbinols; phenyl naphthyl carbinol; diphenyl ethyl carbinol; dixylyl isobutyl carbinol; di-(trimethylphenyl)amyl carbinol; triphenyl carbinol; tricumenyl carbinol; the trinaphthyl carbinols; and in general carbinols having the formula R R R COH, where R is aryl or alkaryl and each of R and R is hydrogen, lower alkyl (i.e. C -C alkyls), aryl or alkaryl.

The chief thermal decomposition products of alkyllead compounds are lead metal and hydrocarbon gas. Hence, a very good index of alkyllead thermal decomposition is liberation of this gas.

To illustrate the effectiveness of this invention, direct comparisons were made between the decomposition characteristics of unstabilized and stabilized tetraethyllead. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction 'tube. A 100 cc. gas buret beside the bath, and equipped with a Water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steady temperature of 160 C., the sample-containing tube was quickly immersed in the bath and clamped with the levelling bottle adjusted to hold the gas buret in place at a zero reading. Then measured was the time during which the sample was held at 160 C. without pronounced thermal decomposition and consequent gas evolution occurring. Thus, the longer the time, the more thermally stable was the alkyllead composition.

With pure tetraethyllead used in 1 ml. amounts, pronounced thermal deterioration occurred within 1 minute as evidenced by rapid gas evolution. In fact, the decomposition of unstabilized tetraethyllead will normally become uncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possible to very rapidly cool it down to about 100 C. or below.

However, when to the same amount of tetraethyllead there was previously added 2 percent by weight of triphenyl carbinol no pronounced deterioration occurred at 160 C. for over 50 minutes. The same order of effectiveness subsists when repeating this experiment using in one instance 1 percent by weight of di-l-naphthyl carbinol, and in another instance percent by weight of phenyl carbinol. In fact, comparable effectiveness is exhibited by all of the thermal stabilizers of this invention.

The above-described beneficial behavior of the thermal stabilizers of this invention also takes place with other alkyllead compounds such as triethyllead bromide and tetra-propyllead. In fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapted to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess alkyl halide have been discharged from the autoclave. For example, one of the above thermal stabilizers may be added in appropriate quantity to the alkyllead reaction concentrate just before the separation step which is constructed at a temperature close to the temperature where hazardous tun-away decomposition is particularly prevalent. By adding one of the above thermal stabilizers to the reaction concentrate just prior to distillation, the danger arising from unexpected temperature increases is substantially eliminated.

Most preferably the above thermal stabilizers are employed to stabilize the alkyllead compound both in storage and in shipping and especially to stabilize any alkyllead concentrate, i.e., compositions containing at least 80 percent by weight of alkyllead compound. If elevated temperature conditions are likely to be encountered, the addition of a small amount of thermal stabilizer to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved. While meticulous temperature control and exacting safety measures have been successful in reducing to a minimum the hazards of processing and handling of tetraethyllead, the use of this invention provides a much greater factor of safety. Furthermore, waste of the alkyllead product due to decomposition is considerably minimized through the use of this invention.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead'is'satisfied by an alkyl radical. For example tetraethyllead, tetramethyllead, tetrapropyllead, dimethyldiethyllead, triethylphenyllead, and tn'ethyllead bromide can be successfully stabilized against thermal decomposition by'incorporating therein a relatively small quantity of one of the thermal stabilizers of this invention.

What is claimed is: I

1. A method of inhibiting the decomposition of an alkyllead compound at temperatures of from about C. to about C. which comprises incorporating with said compound a small amount of an aryl carbinol suflicient to inhibit such decomposition, said aryl carbinol containing from 7 to about 30 carbon atoms in the molecule and having the formula wherein R is selected from the group consisting of aryl andalkaryl, and each of R and R is selected from the group consisting of hydrogen, lower alkyl, aryl and alkaryl.

2. In the. process of producing an alkyllead compound by. reacting a sodium lead alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation in the presence of a small amount of an aryl carbinol as defined in claim 1 sufficient to inhibit thermal decomposition of the alkyllead compound. i i

3. An alkyllead compound containing, in amount sufficient to inhibit thermal deterioration thereof at tempera tures from about 100 C. to about 160 C., and an aryl carbinol as defined in claim 1.

4. Tetraethyllead containing a small amount of triphenyl carbinol suflicient to inhibit thermal deterioration of the tetraethyllead at temperatures from about 100? C. to about 160 C.

2,660,592 Calingaert- -2 Nov. 24, 1953- Krohn Dec. 13, 1955 

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUND AT TEMPERATURES OF FROM ABOUT 100* C. TO ABOUT 160*C. WHICH COMPRISES INCORPORATING WITH SAID COMPOUND A SMALL AMOUNT OF AN ARYL CARBINOL SUFFICIENT TO INHIBIT SUCH DECOMPOSITION, SAID ARYL CARBINOL CONTAINING FROM 7 TO ABOUT 30 CARBON ATOMS IN THE MOLECULE AND HAVING THE FORMULA 